His advocacy of same-sex marriage began well before his White House years, tracing back to his early political service in Illinois. The effectiveness of his leadership, however, will be determined by the U.S. Supreme Court as it considers a California ban on same-sex marriage.

1996: While running for the Illinois Senate, Obama signs a questionnaire for a gay Chicago publication saying he favors legalizing same-sex marriages. He later wins the race.

1998: He alters course and answers "undecided" on same-sex marriage when questioned in another survey.

2003: In his campaign for the Illinois Senate, Obama says in a questionnaire that he is against repealing the Defense of Marriage Act, a 1996 federal law that states for federal purposes, marriage is defined as only between one man and one woman.

February 2011: The Obama administration instructs the U.S. Justice Department to stop defending the constitutionality of the Defense of Marriage Act in court.

June 2011: White House Communications Director Dan Pfeiffer says President Obama's 1996 questionnaire was "actually filled out by someone else, not the president." Obama "has been against" same-sex marriage, but his and the country's position was evolving on the matter, Pfeiffer says. "I can't tell you when that evolution will continue."

2012: Obama endorses same-sex marriage, the first such statement by a sitting president. The legal decision should be up to the states to determine, he says.

January 2013: Obama becomes the first U.S. president to mention gays and lesbians in an inaugural address and champions same-sex marriage.

March 2013: Obama personally reviews and OKs his administration's amicus or "friend of the court" brief filed with the U.S. Supreme Court as it weighs the constitutionality of California's 2008 Proposition 8 referendum banning same-sex marriage.

2013-2017: Will Obama's next evolutionary step seek change in the 41 states that currently define marriage as between one man and one woman? As a second-term president, he certainly has the clout.